Rheumatoid factor (RF) is found at some stage in serum from about 80% of patients with various neoplasms. This project is to expand upon our preliminary results which suggest RF may have relevance to tumor- host interaction. The effect of serum from cancer patients upon the release of Cr51 label from membranes of incubated tumor cells will be studied further (see Appendix 1). The relationship between this Cr51 release and the presence and titer of RF test sera will be analyzed. RF-positive serum autologous to the Cr51 tumor cells, RF-positive serum from patients with different primary neoplasms, and RF-positive serum from patients with rheumatoid arthritis will be tested so as to evaluate the specificity of RF-related Cr51 release. RF-negative serum and RF- positive serum, from which RF is adsorbed, obtained from cancer patients will be tested to see if it is RF or another coexistent serum factor that causes Cr51 release from the membranes of incubated tumor cells. RF binds to IgG. Presumably then, IgG coated tumor cells would have superior affinity for RF binding which, in turn, would augment complement attachment and activity against tumor cells. Tumor cells from RF seropositive and RF seronegative patients will be tested in vitro using immunofluorescent techniques for membrane IgG coating and for C3 attachment from incubation media.